Messerschmitt M23b (oz2459)

About this Plan

Messerschmitt M23b. Jumbo scale rubber model of the 1930 German two seater sport trainer. MB 10-76. Scale is 1/12.

Quote: "Messerschmitt M23b, by Bill Noonan.

A perfect model for the new 36 in minimum wingspan Jumbo scale rules, this ship embodies all the characteristics of our historic rubber scale era that is making such a tremendous comeback.

The Messerschmitt M23 series was introduced with the model 'a' in 1929, to satisfy an appeal issued by the German Aero Club for lightplane designs to compete in the Ostpreussenflug, or Circuit of East Prussia touring contest. The early 'a' model sported the popular ABC Scorpion two-cylinder (38 hp) engine, or the 45 hp Salrnson AD9. The acceptance of the clean, graceful low-wing two-seater encouraged Messerschmitt to make improvements in the form of the M23b, with modified airframe and power plant choices giving pilots no less than eight different engines to choose from. It is interesting to note variations in fuselage length on production models in the 'b' series which varied from 20 feet, 10 inches to 21 feet, 9-3/4 inches. One can assume this had to do with power and weight characteristics.

Our model reproduces the acrobatic mode which served champion Willi Stor [Wilhelm Stör] so well, registered D-1856. It was powered with an 110 hp inverted Argus engine.

No record seems to have been kept of the exact color of the aircraft, but contemporary black and white photo-graphs, probably taken with orthochro-matic film, suggest the plane might have been red and white, which seems appro-priate to the somewhat flamboyant scheme chosen by Star to embelish wings, fuselage and tail surfaces. It must have been popular at air shows.

History records some M23b's with squared-off tail surfaces. Our model follows Star's configuration, which had rounded tips on both stabilizer and vertical fin, harmonizing nicely with the wing plan. This model seems to depart from others also in the aileron design, which, rather than being contained between rib stations, went to the tip radius. The M23 series, particularly the 'c' model, excite a note of familiarity, much as might be elicited by looking through an old family photo album. Deju vu? No, its a reflection of the most famous Messerschmitt of all, the Me109. Subtle qualities in the shape of the wing, fuselage contour, etc. tie these two generations together, revealing the lineage, much the way the photo album might have.

WING: As was the prevailing practice of many German designers of the twenties (Fokker, Junkers, et al) the M23b featured a strongly tapered, deep-sectioned, undercambered wing. We have deviated from the original, not in plan, but mechanically, in the interest of strength. The original had right and left folding wing panels. Our model incorporates a full-span wing, which passes under the fuselage.

Spar is cut from straight-grained 1/8 x 1/2 medium hard balsa, tapered per drawing. Ribs are cut from light 1/16 sheet, omitting spar, leading and trailing edge provisions.

Cut tapered leading edge and roughly sectioned trailing edge. Pin both over respective positions on Saran Wrap-protected plans. The leading edge will need scrap balsa shims to elevate it above the plan to anticipate coinciding with rib contour. Take each rib and hold it in position at its correct station. Confirm proper chord and make mark with sharp cutting tool on each rib at 1.e. and Le. contact points. Cut off surplus and again confirm fit by wedging dry ribs between 1.e, and Le. At this time lay spar across ribs and repeat marking procedure on the top of each rib, indicating spar notch. Withdraw ribs, cut notches to correct depth. Spar sits 1/32 below top of ribs. The excess in front of the spar is removed after assembly, with a fine sanding block. maintaining airfoil contour to the lead-ing edge, This step-down from spar for-ward allows later placement of 1132 balsa leading airfoil edge covering. Cut tips from 1/8 medium balsa, cement in place, trim and sand to proper contour.

Your wings should appear as finished, except for the center section and addition of 1/32 sheet. It might be pointed out at this time that the ailerons were incorporated to enhance the scale effect, as well as to provide for wash-out or to correct incorrigible warps. On the original model, they remain in a fixed position.

Remove wings from plan. Cut dihedral spar brace (part SB) from 1/32 plywood. Cement this part to front of spars, making sure spars accurately parallel brace angle, which automatically gives proper dihedral. Use clothes pins or spring clips available at stationnery supply stores, to hold the whole ball of wax together while it dries. The center section immediately under the fuselage is flat as viewed from the front. This allows the wing to 'cradle' into the bottom of the fuselage.

Add center section ribs as shown, as well as leading and trailing edges. Sand to proper airfoil. The center section will be covered with 1/32 sheet full chord, so no step-down is called for on center section ribs (two). Rather, these two ribs are 1/32 less in depth than adjacent root ribs. False 'stringer ribs' are cemented inside root ribs to form shelf to glue 1/32 sheet to. The 1/32 sheet can now be fitted. Start by running bead of cement (we used Titebond) along top of spar, taking care riot to slop any aft on top of ribs. Pin the sheet along spar top from root rib to tip. When dry, bend to conform to airfoil, and cement to leading edge, When this is dry, cut and sand, feathering to airfoil shape along leading
edge.

Before covering the center section with 1/32 sheet, bend right and left wing anchor hooks and epoxy to back of spar. These will protrude about 3/8 above the 1/32 sheet center section covering which forms the cockpit floor. Mating hooks will later be epoxied inside fuselage sides approximately at top longeron. Stretched rubber bands or tensions springs between the hook sets form the method of holding the wing in place..."

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